Internal combustion engines typically employ either a wet sump or a dry sump lubrication system. Conventional wet sump systems generally include a crankcase, an oil pan defining a sump below the crankcase, and an oil pump. Oil from the crankcase above the oil pan typically flows through a centrally located opening and collects within the pan. The pump is generally centrally located near the bottom of the pan for withdrawing oil from the pan and for supplying the oil to the engine.
During operation of the engine, the oil frequently becomes hot and highly aerated. Because internal combustion engines employing wet sump systems are generally water cooled, the elevated temperature of the oil is of minimal concern. However, the aeration or foaming of the oil affects the oil's performance in lubricating the engine.
In contrast to wet sump systems, dry sump systems may include an oil pan mounted below the transmission case or an exterior oil tank. As a result, oil is usually supplied to the oil pan through an oil return port located at one end of the pan and is usually returned to the engine through a separate oil pickup port located at another location on the oil pan. To prevent premature wear of engine parts, it is desirable to adequately cool the oil before it is returned to the engine through the oil pickup port.
In one type of motorcycle, the oil return port and oil pickup port are located near the same end of the oil pan. In this design, hot oil flowing through the oil return port from the engine can flow directly to the oil pickup port before being adequately cooled within the oil pan. As a result, the internal combustion engine would often not be adequately cooled by the oil supply.